Laundry dryer



Feb. 1, 1966 3,232,591

R. B. WILEY, JR

LAUNDRY DRYER Filed May 23. 1963 2 Sheets-Sheet 1 Richard B. Wiley, Jr.

'Jaw/M Y ATTORNEYS Feb. 1, 1966 R. B. WILEY, JR 3,232,591

LAUNDRY DRYER Filed May 23, 1965 2 Sheets-Sheet 2 FIG.6.

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J J/J Richard B WlihlZ/IR A'ITORNEY United States Patent O 3,232,591 LAUNDRY DRYER Richard B. Wiley, Jr., 141 NW. 24th Ave., Miami, Fla. Filed May 23, 1963, Ser. No. 284,285 Ciairns. (Ci. 263-33) This is a continuation-in-part of application Serial No. 132,499, filed August 18, 1961, now abandoned.

This invention relates to laundry dryers, an-d more particularly to air dryers in which air is rst preheated by contacting the outer surfaces of a conduit internally heated by combustion gases and then further heated to its desired temperature by passing it through tubes which have a major portion of their outer surface in contact with the interior of the conduit.

In open flame types of laundry dryers, such as gas red, the burners are encased and mounted on top of a dryer chamber and, when the gas is ignited, the air is fandrawn through the encasement and over the exposed ilame. The flame-heated air is passed into the dryer chamber where it comes in contact with articles to be dried.

This invention contemplates an improved laundry dryer having a dryer head in which is positioned a conduit fol-l lowing a circuitous path through which are passed combustion gases. Air from outside the dryer head is convectively fan-drawn over a portion of the outer wall surfaces of the conduit out of direct contact with the combustion gases and is first preheated by the transfer of heat through the Wall of the conduit. This preheated air is then passed through a series of heating tubes which extend through the conduit where it is further heated to the desired temperature before being passed into the dryer chamber. The heating tubes have a major portion of their outer surfaces in direct contact with the hot combustion gases so that maximum heat transfer is effective to the preheated air passing therethrough.

The dryer head of this invention allows for higher air heating eiciency because of the use of high heat, low grade combustion fuels, such as oil, as well as cleanness of the heated air since there is no direct contact between the air and the combustion gases.

The conduit may be formed from sheet material having a high heat transfer coecient, such as stainless steel, and constructed to follow a particular path arrangement. The conduit may be in the form of a rectangular box having spaced inlet and exit openings positioned in one end wall with a partition dividing the box into two connecting chambers so that hot combustion gases passing through the inlet flows through one chamber and are directed by turning baffles, 180 Where they flow through the connecting chamber and out of the exit opening. In this arrangement the heating tubes extending through the conduit are positioned in the chamber having the exit opening so that the direct ame does not come in contact with the tubes, being separated therefrom by the partition; and the exit ends of the tubes are positioned so that the air passing therethrough is directed into the dryer chamber.

Advantageously the slots for the intake of air may be positioned in the sides of the dryer head which surrounds the conduit so that the air is forced into contact with a maximum portion of the heated exterior surfaces of the conduit. This positioning results in the air being preheated between the wall of the dryer head and the outer walls of the conduit before it is drawn through the heating tubes.

Preferably the air intake slots may be positioned at the lowest area of vertical sides of the dryer head so that air being drawn through the dryer head is convectively distributed over the side walls of the conduit, thereby eliminating unheated pockets and thus producing uniformly preheated air. The intake slots may be of differing sizes 3,232,591 Patented Feb. 1, 1966 ICC and dimensions, depending on whether these are adjacent to hotter or to cooler sections of the conduit so as to cause a relatively greater amount of incoming air to pass over hotter portions of the conduit and relatively smaller quantities of air to pass over cooler surfaces of the conduit to produce even heat transfer which results in uniformly preheated air. The air passing through the heating tubes exits into `a centralized plenum chamber positioned over the dryer. The bottom portion of the plenum chamber has a centralized slot communicating with the dryer through which heated air is directed into the drying chamber.

Advantageously, the plenum chamber may have intake orifices or slots therein for admitting unheated or cooling air into it so that the plate forming the top of the plenum chamber, which is in direct contact with the bottom of the dryer head, will be prevented from buckling from overheating as the hot combustion gases pass over it. This arrangement of cooling air intake orifices facilitate convective mixing which results in maintenance of a uniformly heated air in the plenum chamber.

It will be appreciated that Where high temperatures are used such as for high temperature drying, the corners or the side Walls, particularly in the area of the top of the plenum chamber where the hot combustion gases are circulating, will be subject to expansion stresses so that buckling of the top plate may occur.

To avoid this buckling the orifices for admitting unheated air, to provide convective mixing, may be positioned in one or more of the vertical Walls of the plenum chamber at various positions and so spaced as t-o produce the maximum eliiciency in air mixing within the chamber.

Exemplary of an orifice arrangement which may be used to prevent hot air spots from forming adjacent to the top of the plenum chamber, is the placement of a series of orifices in at least one vertical wall of the plenum chamber.v It will be appreciated that these orifices may be of any desired size or shape; the total cross-Sectional area then being so regulated to admit the desired amountv of cooling air so as to produce convective mixing and the evening out of the temperature of any hot spots in theplenum chamber.

In another form of this invention, the orifices may be provided in the top plate of the plenum chamber which forms the bottom of the dryer head and positioned in the area Where intake air is being brought into the dryer head for passage through the heating tubes so that a portion `of this air is diverted through the orifices into the plenum chamber to effect a cooling of the hot spots and a convective mixing within the plenum chamber to bring about an evening of the temperature. These orifices, of course, may be of various sizes and arrangements and positioned so that they equalize the temperature in the top plate of the plenum chamber at the point where it is under severest stress from uneven heating by the passage of the combustion gases over it in the dryer head positioned directly above the plate.

In yet another form of the invention, increased convective mixing and consequent cooling of the top plate of the plenum chamber, may be achieved by passing the heated air from the plenum chamber into the dryer chamber through a plurality of slots which may be uniformly spaced or otherwise arranged in the plate forming the top of the dryer chamber and the bottom plate of the plenum chamber. 'I'hese slots may differ in size or placement as most advantageous to achieving evenly distributed temperatures in the plenum chamber.

Also, the air inlet orices in the plenum chamber may be provided with louvres, vanes, or baffles for controlling the quality of air W through the orifices and to give it a ydesired direction of movement. In addition, the size, shape, and placement of the orifices may be arranged so that the desired quantity ot cool air may be admitted to the hot spots in the plenum chamber to elect both a convective mixing and a reduction in temperature of the top plate of the plenum chamber.

The conduit may be heated by a conventional combustion gas-producing means such as an oil burner or the like. It will be appreciated that the cross-sectional area of the combustion chamber of the conduit, the cross-sectional area of the heat exchanger portion of the conduit; the number, cross-sectional area, conguration and placement of the air heating tubes in the conduit, as well as the positioning of the tubes relative to each other, will depend upon the heat content of the combustion gas-producing medium, the rate of iiow of the Vcombustion gases, the heat transfer through the wall of the conduit, and the amount of air being passed convectively in contact with the outer surface of the conduit wall as well as through the tubes and the length of the conduit and tubes.

The laundry dryer of this invention can be so icontrolled that the pressing of a starter or the insertion of a coin will energize a system so that the combustion medium will ignite to produce a continuous flow of combustion gases to heat the conduit, the fan will operate to draw air through the intake slots where it is preheated by contact with the hot wall of the conduit then heated to its maxim-um by passing through the heating tubes positioned in the conduit. The heated air is passed into the drying chamber containing a tumbling device which rotates so that the delivered heated air will contact the articles to be dried to perform a drying function, after which the air is exhausted to the atmosphere.

VvThese and other objects of this invention will become apparent from an examination of the drawings, description and claims.

The invention will be described further in connection with the accompanying drawings which are to be considered as an exempliicaton of the invention and do not constitute limitations thereof.

In the drawings:

FIGURE l is a rear view in perspective showing the dryer head of this invention in place on a typical laundry dr er;

yFIGURE 2 is a plan view of the dryerhead showing the fuel burners, combustion chamber, heating tubes, the bafes, and the combustion gas flow path;

FIGURE 3 is a rear View in elevation ot the dryer head positioned over a dryer chamber showing the combustion gas conduit, the heating tubes, and the intake and exit air ow arrangement;

FIGURE 4 is a cross-sectional view along line 4*4 of FIGURE 2, showing the air flow path overl the walls of the conduit and through the heating tubes;

FIGURE 5 is a View in perspective of the dryer head showing the relative position of the combustion chamber, heating tubes, the combustion gas inlet and exit openings, and the air intake slots;

FIGURE 6 is a vertical view in cross-section of a portion of the dryer head and plenum chamber shown in FIGURE 4 in which the vertical wall of the plenum chamber has rectangular oriiices therein for admitting cooling air to the plenum chamber;

FIGURE 7 is a plan view in cross-section of a portion ot the dryer shown in- FIGURE 3 in which the top plate of the plenum chamber has rectangular orices in it for admitting cooling air therethrough to the plenum chamber; and H FIGURE 8 is a plan view in cross-section showing slots positioned in the bottom plate of the plenum chamber to facilitate convective mixing within the chamber before the heated air is passed into the drying chamber.

Referring to the drawings, FIGURE 1 shows a typical dryer 10 of this invention. The dryer has a head 11 in the form of a rectangular encasement 12 having opposite side walls 13 and 14, front and back end walls 1S and 16, and top wall 17. Encasement 12 is mounted on a drying chamber 18, which has a conventional article tumbling unit 18a (as seen in part in FIGURE 1).

A rectangular heat transfer conduit V19 is positioned within the encasement having -a bottom plate 20, opposite side walls 21, 22, front and back end walls 23, 24, and top wall 25. Positioned in side walls 13 and 14 and front end wall 1S of the encasement are rectangular slots 26, 27, and 2S, which allow for the intake of air substantially in line with bottom plate 23 of the conduit.

The position of the conduit in the encasement provides air passage spaces between the sides, ends and top walls of the conduit and the encasement. IIhe interior of the conduit is in the form of two connecting chambers 29 and 30, separated by a bathe wall 31. A combustion gas inlet opening 32 is positioned in end wall 24 and extends through wall 16 of the encasement to provide a direct passageway for the admission of combustion gases into chamber 29 of the conduit. A conventional type oil burner 32a is attached to or positioned in opening 32. Similarly, a combustion gas exit opening 33 Iis positioned in end wall 24 and extends outwardly through wall 16 of the encasement to permit spent gases to escape from chamber 3@ to the atmosphere. (See FIGURES 2. and 5.)

Positioned within the conduit 19 are curved balli-es 34 which direct the hot combustion -gases through the conduit, turning the gases as they pass from chamber 29 into chamber 30. In chamber 30 lare a group `of staggered ai-rheating tubes 35 which extend from the top wall 25 to the bottom plate 28 and provide for a passage of air therethrough, the exterior surfaces of the tubes 35 being exposed to the flow :of combustion gases passing through the conduit. Air enters the tubes after owing over the top wall 25 fand exits from the bottom of the tubes below the bottom plate Ztl. Below the bottom mediate connective passageway between dryer head 11 and drying chamber 1S for 'admission to said drying champlate is a heated air plenum space 36 which is an interlber of heated air passing through tubes 35. Positioned centrally with respect toV sides 13 and 14 but in the top of dryer assembly 1t) is an opening 37 for entrance of heated air from plenum space 36 into drying chamber 18. Air drawn in through slots 26, 27, and 28 is forced through the air spaces which separate conduit 19 from encasement 12 and up over walls 21, 22, 23, and 24 and into the air space above top wall Z5 to give the air its preheat. This preheated air is drawn down through tubes 35, the outsidepsurtaces yof which are in the path of the combustion gases flowing through 4chamber 30 and Ais heated to its desired extent as it exits from tubes 35 into plenum space 36, from which it passes through opening '37 to the drying chamber. (See FIGURE 4.)

At the lower porti-on of the dryer 10 is a tumbler drive and suction :fan motor 38. The motor driven fan '38a draws air from the atmosphere through intake slots 26, 27 and 28, over the walls of conduit 19 where it is preheated, through the tubes where it is further heated, and through opening 37. The heated lair is then drawn through tumbling articles andexhausts at the bottom portion of dryer 10 through exhaust port 39 (see FIGURE l).

It will be appreciated that the particular combustion gas flow path of conduit 19 and the particular air flow path around `and over conduit 19 of air entering inlet slots 26, 27 and 28 combine to produce pre-heating of the incoming air by rst passing the air up 4over walls 21, 22, 23 and 24 to the space above top wall 25 yof conduit 19.

It is to be particularly noted that .air inlet slots 26, 27 land 2S may be sized in respect to each other and with relation to the respective surface areas and surface teme peratures of the portions of the conduit to which each air inlet supplies outside air so that uniformity and eiliciency in pre-heating the incoming air is eiected. Thus,

air inlet 2.7 which supplies air to the exterior surfaces of chamber 30 of conduit 19 may be smaller than one =or the other of inlets 26 and 2S, which supply incoming air over relatively hotter sections of conduit 19. Likewise, inlet 28 may be smaller than inlet 26.

It will Efurther 'be appreciated that the encasement 12, spaced from conduit 19 whose upper sides it surrounds, the position and sizes of the air intake slots, the position of the chambers 29 and 30 relative to each other, the positioning, number, diameter and length of the air tubes in the conduit and the position of the dryer head adjacent and above the top central intake slot of the drying chamber produce a maximum of air convection so that a high heat transfer is maintained between the air and the wall and tube surfaces of the conduit as well as a conservation of heat produced within the conduit. The air is maintained at a high temperature in its passage through the plenum space 36 lby contact with bottom plate Ztl and is at its maximum controlled temperature when it exits through opening 37.

Alternate arrangements of the dryer device of this invention are .shown in FIGURES 6, 7, and 8. In FIGURE 6, the plenum space or chamber 36 is provided with oriiices 40 through one or more of its vertical walls so that cooling air may be drawn through them. The orifices m-ay be of any desired conguration and variously positioned such as near the top of the walls so that the cooling air when admitted can mix convectively with the hot air in contact with the bottom plate to prevent uneven heating or overheating of this surface.

In FIGURE 7 is another alternate arrangement showing orifices 42 positioned in top plate 20 to provide Ifor the by-passing of a portion of the air from the dryer head before it passes through the heating tubes 35, thereby permitting air to be drawn into the plenum space through these oriiices to ind-nce air circulation in the plenum space and prevent overheating and, consequently, buckling of the top plate 2li of the plenum chamber.

Also, as shown in FIGURE 8, the bottom of the plenum chamber 36 may have a plurality of slots 45. These slots may be so arranged so as to effect turbulence within the plenum space so that air therein is convectively mixed and hot air pockets are eliminated. This mixing prevents top -plate 20 from overheating. It will be appreciated that slots 45 may be of any appropriate size, configuration, and arrangement that will provide for the convective mixing while permitting suiiicient air to pass through the slots to eiect the desired temperature and air flowing through the dryer chamber.

It will also be appreciated that the dryer device of this invention may include oriiices in both the side walls ani in the top plate 20 which form the plenum chamber, and, if desired, the orifices in the side walls or inthe top plate or both, may be used in combination with the slot spacing in the bottom of the plenum chamber to produce lconvective mixing of the heated air coming lfrom the dryer head so that air at substantially uniform temperature is passed through the dryer body as well as preventing hot spots which, in high temperature drying, cause the buckling of the top plate which forms the top of the plenum chamber.

In operation, the oil burner 32a which may be a highpressure flange-mounted gun type and attached to opening 32 res through it and into Ichamber 29 where the hot gases 4of combustion are conducted through conduit 19 and exit at opening 33. The burner may be energized when a coin is inserted in a control slot which sets the whole unit in operation. The burner is controlled by a thermostat so as to assure the maximum eiiicient temperature in the dryer. In addition, a stack switch may be provided in a ue (not shown) connected to exit opening 33 for safety so that the maximum flue temperature will not be exceeded. Upon ring of the burner, the dryer fan motor starts, which also causes the tumbler (not shown) to rotate. The fan motor draws air from the atmosphere into the dryer head through slots 26, 27 and 28 which air passes over the exterior conduit walls and then through the tubes in heated conduit 19, where it is heated and directed through opening 37 and around the tumbler .and finally exhausted through port 39 which may be connected to the outside through a suitable duct.

Where inlet air orifices are provided through the plenum walls, cooling air is drawn through these orifices into the plenum space and convectively mixes with the heated air passing through hea-ting tubes 35. This mixing provides for a more even temperature of the air in the .plenum chamber and thus eliminates the hot air spots which are normally present in the area of the top plate 20 over which the hot combustion gasespass while being employed to heat the heating tubes 35. When a plurality of slots 45 are used, the air drawn through the plenum chamber will be moved convectively therein to cool lthe top plate 20, thus reducing the likelihood that the air will be unevenly heated within the plenum space.

While the novel features of the invention have beenk shown and described and are pointed out in the annexed claims, it is to beunderstood that various omissions, substitutions and changes in construction and arrangement of the parts shown and described may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A dryer head assembly for heated air in combination with a drying chamber to eifect drying of articles therein comprising an encasement having top and side walls, a conduit having a circuitous path positioned within the contines of said encasement, the conduit and walled area definingv an air space therebetween, said conduit having inlet and exit openings extending through the closed walls of said encasement; a combustion gas producing means operatively connected to said inlet opening for injecting hot combustion gases through said conduit and out of said exit opening; air inlet meansfor admitting air'from outside said encasement to said air space; an air plenum chamber positioned below said conduit and having side Walls Vand at least one opening in communica-tion with` said drying chamber; and at least one air-heating passageway extending through said conduit for conducting air from said air space therethrough, the outside wall of each of said air-heating passageway .positioned inthe path of said hot combustion gases and 'connecting said air space With said air plenum chamber; said opening being positioned in said air plenum chamber for inducing mixing of the air from said air space whereby uniformly heated air is maintained in said plenum chamber before passing from said plenum chamber to said drying chamber; andv said drying chamber having means for conveying air from outside said encasement, through said air space over said heated conduit, through each of said air-heating passageway and said air plenum chamber into said drying chamber to effect drying of articles in said chamber.

2. The dryer head assembly of claim 1 in which said air inlet means is a plurality of slots, each slot positioned in one of the side walls of said encasement.

3. The dryer head assembly of claim 2 in which each slot is of a size to adm-it a quantity of air such that the temperature of the air admitted through each slot is raised an amount approximately equal to the temperature rise of the air admitted by each of the other slots.

4. The dryer head assembly of claim 1 in which said hot combustion gases injected into said conduit are produced by an oil burner connected to said inlet opening.

5. The dryer head assembly of claim `1 in which said conduit for transferring heat to said air is constructed of stainless steel.

6. The dryer head assembly of claim 1 in which curved bailies are positioned within the conduit to effect a change of direction of the combustion gases yalong the path of said conduit.

7. The dryer head assembly of claim 1 in which said plenum chamber opening is rectangular and positioned centrally with respect to said side walls of said encasement.

8. The dryer head assembly of claim 1 in which the plenum chamber has a plurality of openings arranged to induce convecting mixing in said plenum chamber.

9. The dryer head assembly of claim l in which at least one of the side walls of said plenum chamber has at least one orifice therein to permit the passage of a controlled amount of cooling air from lthe atmosphere into it to effect convective mixing with heated air passing therethrough.

'10. The dryer head assembly of claim 9 in which the plenum chamber has a plurality of openings in communication with said drying chamber arranged to induce convective mixing in said plenum chamber.

11. The dryer head assembly of claim 1 in which said encasement has a bottom plate which for-ms a common wall between the encasement and said plenum chamber, said vplate having at least one orifice therein in communication with said plenum chamber to permit the passage of a controlled amount of cooling air from it into the plenum chamber to induce convective mixing with the heated air passing therethrough whereby buckling of said pla-te caused by overheating is prevented.

12. The dryer head assembly of claim 11 in which the plenum chamber has a plurality of openings in communication with said drying chamber to further induce convective mixing in said plenum chamber.

13. The dryer head assembly of claim 1 in which said encasement has a bottom plate forming a common wall between said encasement and said plenum chamber; at least one of said side walls of the plenum chamber having atleast one orifice therein; the bottom plate also having at least one oric'e therein in communication with said plenum chamber; and said plenum chamber having a plurality of openings in communication with said drying chamber whereby the orices in said side walls and said bottom plate of said encasement and the plurality of openings in said plenum chamber provide for convective mixing of the air ypassing through said plenum chamber 4to control and produce a uniform temperature in an area in the ings in the walls of said encasement, said conduit and encasement whereby buckling of said plate caused by overheating is prevented.

14. A hea-ted air dryer assembly comprising an enclosed unit for drying articles therein, means for moving articles to be dried in said unit; an air exhaust port for removing air from the enclosed unit; a dryer head for heating air comprising an encasement having top and side walls, a conduit having a circuitous .path positioned in said encasement and combustion gas inlet and exit openings in the Walls of said encasement, said conduit and encasement defining an air space therebetween; a combustion gas injecting means operatively connected to said inlet opening for passing hot combustion gases throughy said conduit and out of said exit openings; curved baffle ymeans within said conduit for directing the Viiow of cornbustion gases along a U path in said conduit; air inlet slots positioned in the lower portions of the side Walls of said encasement; at least one Vair-heating passageway extending through said conduit in the exit portion thereof; an enclosed air plenum chamber below the said Vconduit and in communication with said enclosed unit; leach of said passageways connecting said plenum chamber with said air space; and an opening dened in the bottom wall of said air plenum chamber communicating with the interior of said enclosed unit, said opening being positioned to induce mixing of air from said air space whereby uniformly heated air is maintained in the plenum chamber before passing to said enclosed unit; a fan lfor conveying air from the outside of said dryer assembly to the dryer assembly; whereby energizing said fan and article moving means and ign-iting said combustion gas injection means causes air to ilovv through said air inlet openings over the heated conduit and through each of said heated passageways into the air plenum and through the opening in said plenum to said enclosed unit to dry the articles therein.

i5. A heated air dryer assembly comprising a drying chamber to effect drying of articles therein and a dryer head for heating air positioned adjacent to and in communication with said drying chamber; said dryer head comprising an encasement having top and side walls, a conduit having a circuitous path positioned Within the confines of said encasement, the conduit and said encasement deining an air space therebetween, said conduit having inlet and exit openings extending through the walls of said encasement; a combustion gas-producing means operatively connected to said inlet openings for injecting hot combustion gases through said conduit and out of said exit opening; air inlet means for admitting air from outside said encasement to said air space; an air plenum chamber positioned between said air space and said drying chamber, said plenurntchamber being defined bythe side walls of said encasement and an adjacent Wall of said drying chamber; and at leastfone air-heating passageway Vextending through said conduit for conducting air from said air space into said plenum chamber, the outside wall of each of said air-heating `passageways positioned in the path of said hot combustion gases; said adjacent Wall of saiddrying chamber having an `opening positioned centrally of Vsaid plenum chamber for inducing mixing of the air from said air space whereby uniformly heated air is maintained in said plenum chamber before passing to said drying chamber; and said drying chamber having means for drawing air from outside said encasement through said air space over said heated conduit through each of said air-heating passageways and said air plenum chamber .into drying chamber to effect drying of articles in said drying chamber.

References Cited by the Examiner UNITED STATES PATENTS 1,936,003 11/1933 White 126-109 X 2,1G8,'0 33 2/l9 38 Cooper 126-109 2,725,051 11/ 1955 Hauck et al 126-116 2,875,996 3/1959 Hullar 263-33 WILLIAM F. (TDi-EA, Acting Primary Examiner. JOHN i. CAMBY, CHARLES sUKALo, Examiners. 

1. A DRYER HEAD ASSEMBLY FOR HEATED AIR IN COMBINATION WITH A DRYING CHAMBER TO EFFECT DRYING OF ARTICLES THEREIN COMPRISING AN ENCASEMENT HAVING TOP AND SIDE WALLS, A CONDUIT HAVING A CIRCUITOUS PATH POSTIONED WITHIN THE CONFINES OF SAID ENCASEMENT, THE CONDUIT AND WALLED AREA DEDINING AN AIR SPACE THEREBETWEEN, SAID CONDUIT HAVING INLET AND EXIT SPACE OPENING EXTENDING THROUGH THE CLOSED WALLS OF SAID ENCASEMENT; A COMBUSTION GAS PRODUCING MEANS OPERATIVELY CONNECTED TO SAID INLET OPENING FOR INJECTING HOT COMBUSTION GASES THROUGH SAID CONDUIT AND OUT OF SAID EXIT OPENING; AIR INLET MEANS FOR ADMITTING AIR FROM OUTSIDE SAID ENCASEMENT TO SAID AIR SPACE; AN AIR PLENUM CHAMBER POSITIONED BELOW SAID CONDUIT AND HAVING SIDE WALLS AND AT LEAST ONE OPENING IN COMMUNICATION WITH SAID DRYING CHAMBER; AND AT LEAST ONE AIR-HEATING PASSAGEWAY EXTENDING THROUGH SAID CONDUIT FOR CONDUCTING AIR FROM SAID AIR SPACE THERETHOUGH, THE OUTSIDE WALL OF EACH OF SAID AIR-HEATING PASSAGEWAY POSITIONED IN THE PATH OF SAID HOT COMBUSTION GASES AND CONNECTING SAID AIR SPACE WITH SAID AIR PLENUM CHAMBER; SAID OPENING BEING POSITIONED IN SAID AIR PLENUM CHAMBER FOR INDUCING MIXING OF THE AIR FROM SAID AIR SPACE WHEREBY UNIFORMLY HEATED AIR IS MAINTAINTED IN SAID PLENUM CHAMBER BEFORE PASSING FROM SAID PLENUM CHAMBER TO SAID DRYING CHAMBER; AND SAID DRYING CHAMBER HAVING MEANS FOR CONVEYING AIR FROM OUTSIDE SAID ENCASEMENT, THROUGH SAID AIR SPACE OVER SAID HEATED CONDUIT, THROUGH EACH OF SAID AIR-HEATING PASSAGEWAY AND SAID AIR PLENUM CHAMBER INTO SAID DRYING CHAMBER TO EFFECT DRYING OF ARTICLES IN SAID CHAMBER. 